Date of sowing and emergence timing affect growth and development of loblolly pine seedlings

Loblolly pine (Pinus taeda L.) seeds were sown from February to June in Alabama, U.S.A. If sowing was conducted in May or June, seedling emergence was reduced and seedling mortality increased. Seedlings from earlier sowings grew to greater sizes, but seedlings from later sowings grew later into the fall. Within any given sowing date, the earliest seedlings to emerge grew largest. Seedlings from the February sowing formed buds in mid-summer, flushed, and in some instances flushed yet again. However, by early October, not all seedlings from May and June sowings had formed an initial bud.     

Growth and survival of seedlings of various picea species under northern climatic conditions

The main purpose of these studies was to investigate the adaptation of young seedlings of various seed lots of Picea abies (L.) Karst., P. glauca (Moench) Voss, P. x lutzii Little and P. sitchensis (Bong.) Carr. to northern climatic conditions. Effects of temperature and photoperiod on elongation growth and growth cessation were studied under controlled conditions in a phytotron. In addition, growth and survival of the seedlings outdoors at 69°39’ N lat. were followed for two years. Seed lots of /’. abies originated from northern Norway (66° N lat.), those of the other species were from Alaska (between 57°.and 66° N lat.). The critical photoperiod for budset was 19–20 h for seed lots of P. abies. In general, the critical photoperiod for budset increased with increasing latitude of the seed source, but the results indicated a significantly shorter cirtical photoperiod for seed lots from about 60° N lat., <120 m a.s.l. of P. sitchensis (between 12 and 16 h) than for comparable seed lots of P x lutzii (17–18 h) or P. glauca (18 h). The time course of budset under natural light conditions, both in the phytotron and outdoors, generally followed the pattern predicted from the critical photoperiod. However, in P. glauca the budset occurred earlier than in P. abies although the latter had a longer critical photoperiod. Due to the short critical photoperiod and consequently delayed growth cessation and hardening, all seed lots of P. sitchensis (from 58° to 60° N lat.) were severely damaged during winter. Some damage was also observed in P. x lutzii and in P. abies. The optimum temperature for elongation growth was higher for P. sitchensis than for the other species. In the phytotron experiments, seedlings of P. sitchensis grew best at temperatures between 12 and 21°C, but at 9°C the best growth was obtained in some seed lots of P. abies. After two growth seasons outdoors, all seed lots of P. abies were taller than any seed lot of the other species. Also P. glauca seed lots and one seed lot of P. x lutzii showed good growth, and their growth rhythm seemed to be well adapted to the northern conditions.     

The effect of photosynthetic photon flux density on development of frost hardiness in top and roots of Larix leptolepis seedlings

Seedlings of Larix leptolepis were grown in a growth chamber under short day conditions (8 h day) at 4 different photosynthetic photon flux densities (PPFD's). After a period of 8 weeks frost hardiness of the shoot tips and roots, dry matter content, dry weight (dw), content of glucose and starch were determined. The frost hardiness in the shoot tips increased from ‐15°C at a PPFD of 55μmol m^‐2s^‐1 to about ‐35°C at 440 μmol m^‐2s^‐1. No effect of PPFD was found on frost hardiness of the roots. A high PPFD results in a high dry matter content. The effect on dry matter content was most pronounced for the shoot tips and less pronounced for the roots. The total dry weight increased for both root and top with increasing PPFD. The height of the plants increased when the PPFD increased up to 220 μmol m^‐2s^‐1.